Study on the Adsorption Mechanism of Cu by ZnAl-LDH-Containing Exchangeable Interlayer Chloride Ions.

Different Zn/Al ratios of Cl intercalated ZnAl-layered double hydroxide (ZnAl-LDH) were prepared using the coprecipitation method, and their adsorption performance for Cu in aqueous solution was evaluated. The factors affecting adsorption properties, such as dosage, reaction time, and pH, were determined by adsorption experiments. Then, the adsorption kinetics and isotherm models were fitted to evaluate the adsorption mechanism. The results show that the Zn/Al ratio has a great influence on the adsorption effect, the best adsorption effect is obtained when the Zn/Al ratio is 4:1, and the maximum adsorption capacity of Cu is 213 mg/g. The mechanism study shows that the adsorption of Cu by ZnAl-LDH is mainly an isomorphic substitution. Additionally, during the adsorption of CuSO, the presence of SO undergoes interlayer anion exchange with Cl, and the process of SO entering the interlayer facilitates the isomorphic substitution of Cu and Zn. X-ray diffraction (XRD) analysis shows that as the Zn/Al ratio increases, the interlayer spacing of ZnAl-LDH increases, and the crystallinity decreases. The adsorption process conforms to the pseudo-second-order kinetic process and the Langmuir isotherm adsorption model. Therefore, the adsorption type of ZnAl-LDH for Cu is monolayer chemical adsorption. The adsorption thermodynamic results indicate that the adsorption of Cu is a spontaneous endothermic process. The research results revealed the mechanism of ZnAl-LDH adsorbing Cu, providing ideas for removing and recovering copper-containing electroplating wastewater.